Prostanglandin D2 (PGD2) is a cyclooxygenase metabolite of arachidonic acid. It is released from mast and TH2 cells in response to an immunological challenge, and has been implicated in playing a role in different physiological events such as sleep and allergic responses.
Receptors for PGD2 include the “DP” receptor, the chemoattractant receptor-homologous molecule expressed on TH2 cells (“CRTH2”), and the “FP” receptor. These receptors are G-protein coupled receptors activated by PGD2. The CRTH2 receptor and its expression on different cells including human T-helper cells, basophils, and eosinophils are described in Abe, et al., Gene 227:71-77, 1999, Nagata, et al., FEBS Letters 459:195-199, 1999, and Nagata, et al., The Journal of Immunology 162:1278-1286, 1999, describe CRTH2 receptor. Hirai, et al., J. Exp. Med. 193:255-261, 2001, indicates that CRTH2 is a receptor for PGD2.
Th2-polarization has been seen in allergic diseases, such as asthma, allergic rhinitis, atopic dermatitis and allergic conjunctivitis (Romagnani S. Immunology Today, 18, 263-266, 1997; Hammad H. et al. Blood, 98, 1135-141 2001). Th2 cells regulate allergic diseases by producing Th2 cytokines, such as IL-4, IL-5 and IL-13 (Oriss et al., J. Immunol., 162, 1999-2007, 1999: Viola et al., Blood, 91, 2223-2230, 1998; Webb et al., J. Immunol., 165, 108-113, 200; Dumont F. J., Exp. Opin. Ther. Pat., 12, 341-367, 2002). These Th2 cytokines directly or indirectly induce migration, activation, priming and prolonged survival of effector cells, such as eosinophils and basophils, in allergic diseases (Sanz et al., J. Immunol., 160, 5637-5645, 1998 Pope et al., J. Allergy Clin. Immunol., 108, 594-601, 2001; Teran L. M., Clin. Exp. Allergy, 29, 287-290, 1999).
Therefore, antagonists which inhibit the binding of CRTH2 and PGD2 should be useful for the treatment of allergic diseases, such as asthma, allergic rhinitis, atopic dermatitis and allergic conjunctivitis.
Ulven and Kostenis, J. Med. Chem., 2005, 48(4):897-900 reports the synthesis of analogs of ramatroban that are selective potent CRTH2 antagonists. CRTH2 antagonists are also reported in patent applications: WO2003/097598, U.S. Pat. Nos. 7,220,760, 7,211,672, 7,166,607, US20070232681, US20070208004, US20070191416, US20070203209, US20070197587, US20070161698, US20070129355, US20060241109, US20060135591, US20060111426, US20060106081, US20060100425, US20060106061, US20050256158, US20060004030, US20050165033, US20050119268, EP147057, EP1556356, EP1784182, EP1833791, EP1814865, EP1828172, EP1761529, EP1758874, EP1756032, EP1718649, EP1675826, EP1633726, EP1556356, WO2006034419, WO2007062678, WO2007062677, WO2006111560, WO2007019675.